Industrial furnaces including, for example, blast furnaces used in the iron and steel industry, require very high temperatures during operation. In order to achieve these temperatures, which may exceed 3,000.degree. F., some preheating of the air entering the furnace is often required. This preheating is typically accomplished using a chamber separate from the furnace, called a "regenerative chamber" or "stove." These stoves are tall, cylindrical steel structures insulated with refractory and mostly filled with refractory checker bricks where heat is stored and then transferred to the air entering the blast furnace. Each stove also includes a combustion chamber used to preheat air before it passes through the refractory checker bricks. Each stove can also operate in a reverse mode wherein combustion is stopped and exhaust air from the furnace passes through the stove.
Referring to FIG. 1, a conventional regenerative chamber 10 is shown in vertical cross-section. The stove 10 includes an outer steel shell 12, and an inner refractory shell 14, both of which are typically cylindrical in shape. The stove 10 also includes a semi-spherical dome-shaped top 16, and a steel/concrete base 18. The refractory shell 14 substantially covers the sides and dome of the stove 10, and is typically constructed of fireclay, high alumina and/or mullire brick.
The inside of the oven 10 includes a combustion chamber 15 and a checker chamber 20. The combustion chamber 15 is lined on its sides by a heavy duty insulating liner 17, typically constructed from alumina brick. During the preheating operation, air enters the combustion chamber 18 through an air inlet 22. The combustion chamber 15 is heated by a burner (not shown) which communicates with the combustion chamber 15 via a separate combustion inlet 24. Air which enters through the inlet 22 is heated and is caused to rise through the chamber 18 into the dome region 26 of the stove 10, whereupon the hot air passes down through the checker chamber 20 and exits through an outlet 30 which communicates with a furnace (not shown). The dome 16 defines the dome region 26, and includes a manhole 28 at its top, which is typically plugged during operation of the stove 10.
FIG. 2 is a sectional view of the stove 10 from just above the combustion chamber and the checker chamber. As shown therein, the majority of the stove 10 is occupied by the checker chamber 20, with the ovular combustion chamber 15 occupying only a minor portion of the stove 10. Also, the refractory liner 14 forms a first wall 23 inside the checker chamber 20, and a second wall 25 surrounding the combustion chamber 15. The combustion chamber 15 is also defined by a separate shell 27.
In the prior art, the checker chamber 20 has been filled from top to bottom with a checker column 21 composed of many layers of checker bricks constructed from a high temperature-resistant refractory material, for example, mullire, high alumina, fireclay, andalucite, or a combination of the foregoing. The checker bricks are available in a wide variety of configurations, for example, the checker bricks 32, 34 and 36 shown in perspective in FIGS. 4, 5 and 6.
The checker bricks include a large number of openings 38 which, in FIG. 2, have been enlarged to simplify the later illustration of the invention. In the checker chamber 20, the checker bricks are placed side by side and in layers, with the layers being lined up so that the openings 38 coincide throughout the length of the checker column 21. Hot air from the combustion chamber 15 passes down through the openings 38 in the checker column 21, causing the checker bricks to heat up and reach a steady state high temperature distribution, assuring a generally uniform temperature for preheated air passing into the furnace from the checker chamber 20 through the outlet 30.
A typical blast furnace is simultaneously connected to three regenerative stoves 10. At any given time, two of the stoves 10 are set up for the forward (preheat) operation and one of the stoves 10 is set up for the reverse (exhaust) operation. During the exhaust operation, the combustion burner is deactivated and the flow through the stove 10 is reversed. Exhaust gases from the furnace enter the stove 10 through the port 30 and rise through the checker column 21, gradually resulting in the cooling of both the exhaust gases and the checker bricks. The exhaust gases then rise into the dome region 26, pass down through the deactivated combustion chamber 15, and exit via the port 22.
As shown in FIG. 1, and more clearly in FIG. 3, the checker column 21 is supported by a porous plate 40 which, in turn, is supported by a rim 41 and a plurality of steel columns or beams 42. Except for the region occupied by the plate 40, rim 41 and beams 42, the checker column 21 occupies substantially the entire height of the stove 10, and also occupies most of its cross-section. Referring to FIG. 1, the height of the checker column 20 may be on the order of 130 feet for a typical blast furnace stove. Referring to FIG. 2, the checker column diameter (left to right) may exceed 30 feet. The diameter of the checker openings 38, by comparison, is typically less than six inches, and the depth of a single checker brick (FIGS. 4-6) is typically about 4-7 inches. Therefore, a very large number of individual checker bricks, positioned in a very large number of layers, are needed to fill a checker chamber 20.
Periodically, the checker bricks in the checker chamber 20 wear out and need to be replaced. Replacement of these checker bricks has been a very labor-intensive, capital-intensive and time consuming process. When replacing the checker bricks, or when installing checker bricks in a new regenerative chamber 10, the checker bricks must be laid out side by side, layer upon layer, until the checker chamber is full. This installation of checker bricks may require several weeks of time and a large quantity of individual, precision-molded, refractory checker bricks.
In order to reduce the cost of relining the checker columns in blast furnace stoves and other regenerative chambers, there is a need or desire for a method which requires less down time and less labor. There is also a need or desire for a checker column which does not require the purchase of large quantities of individual, precision-molded checker bricks and which is, therefore, less expensive, without sacrificing performance.